Experiment 9: Determination of Dissolved Oxygen Flashcards
The acceptable range for environment of this parameter:
pH
6-9
The acceptable range for environment of this parameter:
TSS
Less than 150 ppm
The acceptable range for environment of this parameter:
TDS
Less than 2100 ppm
The acceptable range for environment of this parameter:
DO
4.5-8
The acceptable range for environment of this parameter:
COD
Less than 200 ppm
The acceptable range for environment of this parameter:
BOD
Less than 50 ppm
- refers to the level of free, non – compound oxygen (O2) present in water or other liquids
- oxygen that is bonded in water is a compound oxygen
- high level or low level of DO affects the aquatic life
Dissolved Oxygen
Dissolved oxygen is used for respiration for aquatic life like:
fish,
invertebrates,
bacteria and
Plants
bottom feeders, crabs, oysters and worms need minimal amounts of oxygen
(1-6 mg/L)
while shallow water fish need higher levels
(4-15 mg/L)⁵
Where does DO come from
- photosynthesis
- diffusion from atmosphere
- wind cycling
- 100% air saturation:, equilibrium will occur:
- Photosynthesis occur
- the water will slowly absorb oxygen and other gasses from the atmosphere until it reaches equilibrium at complete saturation.
- use of wind-driven waves and other sources of aeration can speed up the absorption of oxygen.
Upper water
- DO is below 100% due to the respiration of aquatic organisms and microbial decomposition.
- are not shallow enough to be affected by the waves or aeration and photosynthesis at the surface.
- is below an invisible boundary called the thermocline (the depth at which water temperature begins to decline)¹¹.
Deeper water
factors that affects DO
- temperature
- salinity
- pressure
relationship of DO with temperature and salinity
DO decreases as the temperature and
salinity increases
relationship of DO with pressure
DO increases as the pressure increases
Factors affecting DO depletion
- BOD : CBOD & NBOD (pollutants) – waste discharge
- BOD present in the upstream – waste discharge
- DO in the waste discharge
- Nonpoint source pollutants
- Respiration of organisms living in the sediments
- Respiration of aquatic life
Winkler Method or Iodometric Method
Collection of sample:
- Reagent must added immediately to prevent contamination from the atmosphere
- BOD bottle
- titrant needed to complete the reaction is proportional to the dissolved oxygen concentration of the sample
- Time consuming
